When people are looking at Phase I results, it is always worthwhile to put these in context.
Here are two very early Taxol abstracts (the first was cited on the IMGN thread at Ragingbull):
J Clin Oncol 1986 May;4(5):762-6 Related Articles, Books, LinkOut
Phase I study of taxol using a 5-day intermittent schedule.
Legha SS, Tenney DM, Krakoff IR.
Taxol is a plant product derived from the western yew, Taxus brevifolia. We have conducted a phase I clinical study of Taxol used intravenously daily for 5 days at 3-week intervals. The starting dose was 5 mg/m2 daily, and the highest dose used was 40 mg/m2 daily for 5 days. The daily dosage of Taxol was mixed in 250 mL of intravenous fluid and infused over a period of 1 hour. A total of 20 patients with metastatic solid tumors refractory to standard therapy received 45 courses of therapy. Taxol was generally well tolerated and caused no significant nausea or vomiting. A mild degree of diarrhea was reported by six patients, and a moderate degree of stomatitis at the higher dose levels developed in four patients. All patients treated in the dosage range of 20 mg/m2 to 40 mg/m2 experienced nearly complete alopecia. Myelosuppression, predominantly in the form of leukopenia, was the dose-limiting toxicity. The nadir of leukopenia was reached between days 8 and 12 followed by complete recovery between days 15 and 21. Leukopenia was first observed following the Taxol dosage level of 20 mg/m2/d, was moderately severe at the dosage level of 30 mg/m2/d, and was severe at the dosage level of 40 mg/m2/d. No objective tumor regression was observed. A starting dosage level of 30 mg/m2/d for 5 days is recommended for phase II trials using this schedule.
Cancer Treat Rep 1986 May;70(5):605-7 Related Articles, Books, LinkOut
Phase I trial of taxol given as a 3-hour infusion every 21 days.
Kris MG, O'Connell JP, Gralla RJ, Wertheim MS, Parente RM, Schiff PB, Young CW.
Taxol is a unique plant product that promotes in vitro assembly of microtubules. In a phase I trial, adults with advanced solid tumors were given taxol (formulated with cremophor EL and dehydrated alcohol) as a 3-hour iv infusion every 21 days. The total dose administered ranged from 15 to 230 mg/m2 in nine escalation steps. Leukopenia, thrombocytopenia, nausea and vomiting, alopecia, stomatitis, transient rashes, increases in serum triglyceride levels, and hypersensitivity reactions were observed. Hypersensitivity reactions characterized by acute dyspnea, generalized erythema, and hypotension immediately following the initiation of the taxol infusion occurred in three of five patients receiving greater than or equal to 190 mg/m2 (18% of patients overall). No antitumor activity was observed. Hypersensitivity reactions constituted a treatment-limiting toxicity for this preparation of taxol given on this schedule over the dosage range examined. With the severity and unpredictability of the hypersensitivity reactions, further usage of taxol is not indicated with this drug formulation on this administration schedule. Further studies are warranted to uncover ways to permit the safe administration of taxol.
(emphasis added)
Bottom line - it often takes quite a bit of tweaking to get the right dosage regimen, and marginal looking efficacy in an early Phase I can be very misleading.
Of course most drugs with results like these now reside in hazardous waste disposal areas. (Taxol though of course is a $1+ billion drug).
Peter |
